The rolling mill has double high line, single high line, 1# bar line and 2# bar line rolling line, most of which are high strength short stress line mills. The rolling mill adopts the form of horizontal and vertical alternating arrangement on the screen. It produces round steel, rebar steel and some specifications of anchor steel for ∮6 - ∮40, with the designed annual output of 3 million tons.It was successively completed and put into operation in July 2012. In the subsequent production, bearing burning incidents occurred frequently in the rolling mill, and more frequent bearing burning accidents occurred continuously within a week.The newly on-line standby machine sometimes only uses two rolling grooves to burn the bearing and is forced to take it off the line for maintenance, increasing the labor intensity of workers.

1. Rolling bearings are mostly used for the rolls of short-stress rolling mills

Rolling mill bearing burning refers to the phenomenon that the sliding heat of each part increases sharply in the process of running the bearing and plastic deformation causes the parts to bond and excessive wear causes the sticking.Each bearing has a pre-calculated service life. The rolling bearing life used by the rolling mill is the total number of revolutions rotated by the rolling body when fatigue erosion points appear on the raceway or the total number of hours working under a fixed speed.

The failure and damage of the roller bearing caused the auxiliary bearing of the rolling mill to be out of normal use.There are three types of failure of rolling bearings.

（1）Fatigue pitting

Using a period of process, bearing raceway and rolling body under the action of cyclic contact stress, inner and outer raceway or rolling body surface will appear fatigue pitting corrosion damage phenomenon.

 （2）Plastic deformation

Under the action of large static load or impact load, the local stress at the contact point between the rolling body and the raceway may exceed the yield limit of the material, resulting in uneven plastic deformation at the contact point and pits. The phenomenon of increasing rotational resistance and decreasing rotational accuracy makes the noise of the bearing when it is running.

 （3）wear is mainly caused by poor lubrication of bearings and improper sealing or poor working environment, and if the speed is too high, it will produce adhesive damage.

2. The causes of premature failure of bearings are analyzed in the actual use of steel rolling production

About 12% belong to improper assembly and disassembly, and can't use the right tools for disassembly, bearing and the bearing assembly clearance, bearing and the bearing in the process of assembly due to improper operation caused bearing bearing raceway and rolling body is damaged, the right to use tools to install must take the effective and uniform installation force applied to the interference fitted on the shaft of avoid bearing damage.Bearings shall be axially pushed to the appropriate distance on the shaft or bearing pedestal in accordance with the requirements of bearing pedestal and bearing assembly clearance for short strain rolling mills.For bearings, if the clearance between the bearing seat of the roll and the frame column is too large, the rocking of the bearing seat is too large, the bearing will be subjected to large alternating impact load cutting, the working condition will deteriorate, and the service life will be reduced.It affects the positioning of the bearing seat, and then affects the force of the bearing in the bearing seat, and accelerates the damage of the bearing.

About 32% belongs to improper lubrication. The lubrication of bearings is to use the oil film to separate the rolling surfaces in relative motion from each other, to ensure that the performance and rotation accuracy of bearings are stable during working hours, and to avoid bearing passability wear failure or damage.

About 18% belongs to pollution. Oil pollution is caused by damage of oil quality or poor sealing, which worsens the performance of lubrication. The rolling mill rolls are cooled by turbidi-ring water, which easily pollutes the grease and increases the wear and tear of all parts of the bearing, thus affecting the service life of the bearing.

About 38% belong to the improper maintenance of spare parts or neglect of maintenance and bearing overload, high frequency to bear alternating impact load caused fatigue damage.Under the condition of rolling mill creep, pull welding rolling groove causes welding current discharge and damages bearing grease coating, resulting in electrical corrosion of bearing inner passage, uneven bump and dent, increasing the friction during bearing operation, accelerating the uneven wear between bearing inner ring and outer ring as well as between rolling body, which greatly reduces the service life of bearing.

3. In view of the frequent damage of mill bearing pedestal, in the actual production process, the following points can effectively prevent and eliminate the occurrence of burning mill accidents

3.1 Offline assembly and debugging of rolling mill bearings

The rolling mill must focus on the bearing pedestal of the rolling mill for careful inspection, clean, eliminate foreign bodies, before assembly to confirm that there is no foreign bodies and component deformation in the bearing pedestal, according to the tolerance and coordination to determine whether to replace.

Check, clean and lubricate the adjusting device.Because of the dead weight of the bearing seat and the upper roller, the gap between the screw of the pull rod and the press nut is easy to cause a large bounce of the roller, that is, the vibration causes the stress condition of the roller bearing to deteriorate, so it is necessary to ensure the integrity of the roll balancing device of the rolling mill.

Before assembly, make sure that there is no foreign body in the bearing pedestal, the oil seal of the bearing skeleton is intact, the clearance between the rolling body and the raceway meets the requirements, and ensure that the bearing inner sleeve is aligned with the corresponding rolling mill bearing pedestal.The roller neck must be wiped clean, and the surface must not be greasy, protruding and other foreign bodies. The bearing inner sleeve and labyrinth shall be installed after heating, and the heating temperature shall not exceed the specified temperature. The surface finish of the equipment shall not be damaged during the assembly process.After the roller assembly is completed, the rolling mill must be inspected for axial (axial adjustment ±5mm) and radial adjustment, and the assembly and fixation of bearing housing and bearings must be checked according to the process requirements.Ensure that all parts of the rolling mill are in good condition and effectively tightened. Lubricate the lubricated parts to ensure that the roller bearings are effectively lubricated and uniformly stressed within the effective adjustment range.

3.2 On-line assembly and debugging of rolling mill bearings

The on-line assembly of the rolling mill must ensure that the rolling line is horizontal and the effective center line of the hole is perfect, which is the prerequisite to ensure the parallel rotation of the upper and lower rolls and the uniform radial and axial force of the bearing.It is required to check the wear of the slide rail of the rolling mill base and the clamping device of the rolling mill base in advance to prevent the rolling mill from shaking and moving, which may damage the roller bearing by the larger impact load of rolling parts or reduce the service life.

3.3 The bearing pedestals and bearings of the rolling mill should be used online

The staff is required to record the use information of the roller bearing pedestal and bearings, analyze the use of bearings in combination with the actual production, make effective prevention, and replace the failed bearing pedestal and bearings.Perform the standardized operation of the material type, adjust the material type first when adjusting the tension online, and adjust the auxiliary speed until the tension adjustment meets the requirements.Avoid bearing the impact of excessive load, exceeding the bearing material yield limit to produce plastic deformation and form pits and premature failure.

Timely, timely all lubricating points of mill sliding examination and complement operation of grease, forbidden to welding operation of rolling mill, for a long time before the assembled roller bearing to pull the welding groove, welding processing, to test the bearing operating temperature, to look at the outer parts of the bearing, found the abnormal situation analysis and ready for work.

According to the mechanical characteristics of the roller bearing, the rolling speed is controlled to ensure that the roller bearing can operate at a high speed and effectively. The rolling temperature of the billet heating system is controlled reasonably, and the rolling temperature of low-temperature steel and blackhead steel is prohibited to prevent the serious damage of the roller bearing caused by the great deformation resistance of the rolling parts, which affects the normal operation.

Duty personnel operated strictly according to the process procedures, warranty card have been "" three flat, on-line inspection of roll cooling of ontology, to prevent roll by roll surface temperature is too high and the lubrication of the bearing scattered influence bearing lubrication effect, on the operation of the rolled piece shape observation, avoid torsional cause uneven deformation of rolled piece axial force on the roll, harmful influence on the thrust bearing of the bearing.

3.4 Implement the preparation of spare parts

Select high-quality spare parts, screen the use of bearing housing and bearings, timely clean up the failed parts, maintain and protect the spare parts, maintain and protect the spare parts,

3.5 Accident prevention and rectification

For the rolling mill burning bearing accident occurred in the rolling process on duty, in line with the principle that equipment is the basis and operation is the key, the team on duty is required to analyze the accident and organize the production related personnel to study for all the staff.

Improve the assembly operation skills of assembly personnel, strengthen the inspection of rolling mill bearing quality, to ensure that the bearing assembly meets the requirements;Make assembly inspection and handover before rolling mill on-line;Improve the working skill and responsibility of mill adjusting personnel;Carry out lubrication inspection and production process supervision for on-line rolling mill;Do a good spot inspection of equipment and prepare for accidents.